Phase modulation



April 19, 1938. J. w. coNKLlN PHASE MODULATION Filed Jan. 10, 1935lNvENToR J .W. CONKLIN Patented Apr. 19, 1938 UNITED STATES PATENTOlTlCE PHASE MODULATION tion of Delaware Application January 10, 1935,Serial No. 1,115

3 Claims.

This invention relates to a method of producing phase modulation andparticularly to a method of producing phase modulation on lowfrequencies.

The most reliable method of producing phase modulation known at presentconsists of modulating the phase of the output of a constant frequencyoscillator source, such as a piezo-electric oscillator. The modulatingis accomplished at a convenient frequency and the modulated output thenmultiplied to the transmitter frequency. The modulation is multipliedwith the frequency. To obtain any desired degree of modulation, it isonly necessary to start with a low enough oscillator frequency. Thismethod has the advantage over direct methods in that the frequencystability is the same as the oscillator used and can therefore be mademuch more stable than systems working directly on the phase of anoscillator. This system, however, has a limit of modulation at themodulated frequency, theoretically being a maximum of plus or minusninety degrees and practically about ten or fifteen, owing to thecharacteristics of the circuits employed.

When frequency of the source is of such an order that it can bemultiplied many times to the output frequency, the modulation can beincreased in the same order. It is desirable that the source frequencybe considerably greater than the modulation frequency and it istherefore difficult to apply this method to cases where the outputfrequency is low, such as in long wave systems or broadcasttransmitters. Where it is desired to use a quartz oscillator, it is notpractical to construct and operate such oscillators at frequencies belowthe order of 50 to 100 kilocycles. The selectivity of related circuitsalso tends to cut the audio frequency sidebands. The object of mypresent invention is to overcome these practical obstacles. In carryingmy invention into effect, I produce the modulation at a convenientfrequency, multiply it to get the desired degree of modulation, as inthe normal manner, and then employ a suitably stabilized oscillator suchas a piezo-electric oscillator to heterodyne the modulated waves to thetransmitter frequency or to a convenient sub-multiple thereof.

By this method, the system of modulation becomes standardized for alloutput frequencies, whether high or low, and can be transferred from onetransmitter to another by variation of the heterodyning oscillator andoutput circuits alone. The heterodyne oscillator could well be a unit ofthe transmitter rather than the modulator, thereby making it possible tooperate several transmitters simultaneously from the same source, ifdesired.

The accompanying drawing shows schemati- (Cl. Z50-17) cally and in blockdiagram form a way of carrying my present invention into effect.

The super-audible oscillation generator 2 feeds energy into a phasemodulator 4 which is also supplied with waves from any suitable signalsource 6. 'Ihe relatively low, but superaudible frequency phasemodulated output from phase modulator 4l is fed into a suitablefrequency multiplier 8 of any number of stages and with a suflicientfrequency multiplying power such as to produce the desired amount ofphase modulation. The output of frequency multiplier 8 is fed into theheterodyne detector or modulator il) which is also supplied with energyfrom the crystal controlled or other form of constant high frequencyoscillation generator I2. The output of the heterodyne modulator l maythen be fed directly into a power amplifier lil and radiated from asuitable antenna I6. If desired, filter I8 for separating a single sideband may be added, and, if desired, an additional frequency multipliermay be used between the filter i8 and the power amplifier I4. Amplifiersmay be used wherever desired or found necessary.

Having thus described my invention, what I claim is:

1. The method of signaling by phase modulation which includes generatingsuper-audible oscillations, phase modulating the super-audibleoscillations in accordance with a signal, frequency multiplying thephase modulated oscillations, producing constant high frequencyoscillations, heterodyning the phase modulated oscillations with theconstant high frequency oscillations, filtering the resulting energy toobtain sideband energy, frequency multiplying the sideband energy, andtransmitting energy resulting from the frequency multiplying process.

2. Apparatus for transmitting phase modulated waves comprising a sourceof super-audible oscillations, means for phase modulating thesuper-audible oscillations in accordance with a signal, means forfrequency multiplying -the phase modulated oscillations, a source ofhigh frequency oscillations of substantially constant frequency, meansfor heterodyning the high frequency oscillations with the frequencymultiplied phase modulated oscillations, means for selecting from saidheterodyned oscillations a single sideband, and means for transmittingsaid single sideband.

3. Apparatus as claimed in claim 2 characterized by the fact that meansare provided for frequency multiplying the output of saidsidebandselecting means and being characterized by the fact that meansare provided for transmitting the output of said last mentionedfrequency multiplying means.

JAMES W. CONKLIN.

